| Course | PS 101 Psychology |
|---|---|
| Unit | Unit 3 |
| Paper type | Biological basis short paper |
| Length | About 950 words, 6 pages |
| Format | APA 7 student paper |
| School | Herzing University |
| Program | BS in Psychology |
| Updated | October 2026 |
Free sample paper for PS 101 Unit 3
The Growl Before Lunch: Ghrelin, Leptin and the Hypothalamus in the Start and Stop of an Ordinary Meal, and Where the Biology Stops Explaining
Student Name
Psychology, Herzing University
PS 101: Psychology
Instructor Name
January 28, 2026
The Growl Before Lunch: Ghrelin, Leptin and the Hypothalamus in the Start and Stop of an Ordinary Meal, and Where the Biology Stops Explaining
The Behavior
The behavior examined here is ordinary: feeling hungry in the late morning and starting to eat at lunch, then stopping once a meal is finished. It happens every day, it can be observed, and it has a reasonably well studied biological chain behind it. This paper follows that chain only as far as it goes, from the stomach to the brain and back, and then marks the point at which biology stops explaining what happens at the lunch table.
Two Kinds of Signal
The body sends two broad kinds of signal about food. Short-term signals rise and fall around each meal and help decide when to start and stop eating. Long-term signals reflect how much energy the body has stored and shift the overall level of appetite over days and weeks. Morton et al. (2006) describe how the brain integrates both kinds of signal, with a central role for the hypothalamus, a small region at the base of the brain that also helps regulate body temperature, thirst and hormones.
The Short-Term Chain: Ghrelin and Meal Initiation
The hormone
Ghrelin is a hormone produced mainly by cells in the stomach. Unlike most gut hormones, which reduce appetite, ghrelin increases it.
The evidence in humans
Cummings et al. (2001) measured ghrelin in the blood of healthy volunteers who ate meals at fixed times across a day. Ghrelin levels rose before each meal, roughly doubling, and fell within about an hour after eating. Because the rise came before eating rather than after, the authors suggested that ghrelin plays a role in starting meals. The study measured an association in a small group of adults; on its own it shows timing, and other experiments, including studies in which ghrelin was given to people and increased their food intake, supply the causal evidence the course textbook summarizes.
Where it acts
Ghrelin travels in the bloodstream and acts on neurons in the arcuate nucleus of the hypothalamus, a cluster of cells that promotes eating when activated. Morton et al. (2006) describe this cluster as one of the main points where signals from the body are converted into a drive to eat.
Stopping the Meal
The end of a meal involves different signals. As the stomach fills, stretch receptors in its wall send messages to the brainstem through the vagus nerve, and hormones released by the intestine as food arrives reduce appetite. Ghrelin falls at the same time. These signals together make continued eating less rewarding, and the meal ends. This part of the chain is less tidy than the start, because many signals contribute and none of them works alone.
The Long-Term Chain: Leptin and Stored Energy
Leptin is a hormone produced by fat cells, so the amount in the blood roughly reflects how much fat the body stores. Friedman and Halaas (1998) reviewed the discovery of leptin and its role. Mice with a genetic mutation that prevents them from producing leptin eat excessively and become severely obese, and giving them leptin reduces their food intake and body weight. Leptin acts on the hypothalamus too, generally reducing the drive to eat when energy stores are high.
The human story is more complicated. Most people with obesity have high leptin levels rather than low ones, which suggests that the brain becomes less responsive to the signal. Leptin therefore helps explain long-term regulation in principle but does not by itself explain differences in body weight among people.
The Chain in Summary
| Link | Structure or signal | What it contributes | Evidence type |
|---|---|---|---|
| Stomach empties | Ghrelin released by stomach cells | Rises before meals and increases appetite | Human measurement study; other experiments |
| Signal reaches brain | Arcuate nucleus of the hypothalamus | Converts hormonal signals into a drive to eat | Review of animal and human research |
| Meal ends | Stretch receptors, vagus nerve, gut hormones | Reduce appetite as food arrives | Review |
| Energy stores reported | Leptin from fat cells | Lowers appetite over longer periods | Animal genetic studies; review |
Where the Biological Account Runs Out
The chain explains a great deal about why hunger rises before lunch and fades after it. It explains much less about what actually happens at noon. It does not explain why lunch is at noon in the first place, which is a social schedule rather than a biological fact. It does not explain why one person chooses a salad and another a burger, which depends on taste learned over years, culture, price and what is available nearby. It does not explain eating when not hungry, such as finishing popcorn at a movie, which is driven by cues and habits more than by ghrelin. Even the timing of ghrelin is not purely biological in this evidence. The volunteers in Cummings et al. (2001) ate on a fixed schedule, so the rise before each meal may partly reflect when they were used to eating, a question that design could not settle. If so, learning and biology are woven together rather than separate.
The fair conclusion is that biology provides the signal to start and stop eating and the background level of appetite, while psychology, learning and culture shape most of what we eat, when, and how much. A complete explanation of lunch needs both, and this paper has deliberately covered only the first.
Why the Boundary Matters
Marking the boundary is not a technicality. Popular writing often presents hormones as if they were the whole story, as when ghrelin is called the hunger hormone and leptin the fullness hormone, which suggests that appetite could be explained, or fixed, by adjusting two chemicals. The evidence reviewed here supports a narrower claim: these signals contribute to the drive to eat, alongside many others, and their effects depend on a brain that is also responding to habit, setting and expectation. For an introductory psychology student the lesson extends beyond eating. Biological explanations are powerful when they identify a mechanism and the evidence for it, and they become misleading when they are stretched to explain choices that the mechanism does not reach. Being able to say where an explanation stops is part of understanding it.
References
Cummings, D. E., Purnell, J. Q., Frayo, R. S., Schmidova, K., Wisse, B. E., & Weigle, D. S. (2001). A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes, 50(8), 1714-1719. https://doi.org/10.2337/diabetes.50.8.1714
Friedman, J. M., & Halaas, J. L. (1998). Leptin and the regulation of body weight in mammals. Nature, 395(6704), 763-770. https://doi.org/10.1038/27376
Morton, G. J., Cummings, D. E., Baskin, D. G., Barsh, G. S., & Schwartz, M. W. (2006). Central nervous system control of food intake and body weight. Nature, 443(7109), 289-295. https://doi.org/10.1038/nature05026
What the PS 101 Unit 3 instructions ask for
The third PS 101 unit asks for a short paper on the biological basis of one behavior. Expect to name the behavior concretely, follow the nervous system structures and chemical signals involved only as far as the chain requires, use anatomical terms precisely, attach evidence to each link with the type of study named, and close by stating where the biological explanation runs out. Short means focused on one chain rather than brief, so the paper still needs depth. A textbook may be enough for basic anatomy, though instructors usually reward at least one research article. Using your own medical records or anyone else's health information as an example is not appropriate for a class paper.
How the PS 101 Unit 3 example is put together
The paper opens by naming the behavior and the plan to follow one chain. It introduces short-term and long-term signals using a review by Morton and colleagues. The ghrelin section covers the hormone, the human study by Cummings and colleagues with a note on what that design shows, and the hypothalamic target. A section on ending the meal covers stretch receptors, the vagus nerve and gut hormones. The leptin section reports the animal evidence and the complication of resistance in humans. A summary table lists each link, its function and evidence type, and two closing sections mark where biology stops explaining and why that boundary matters.
Reading the PS 101 Unit 3 rubric
Herzing's rubric for the biological basis paper usually awards points for a clearly defined behavior, accurate structures and signals, appropriate evidence with study types, recognition of limits and writing quality. The behavior criterion rewards something observable rather than a vague capacity. Accuracy scores when terms are used at textbook precision. Evidence is often heavily weighted and earns full credit when each link is supported and the type of study is named, since an animal study supports a different claim than a human one. Limits earn points when the paper identifies what the biological account cannot explain. Instructors also credit papers that avoid presenting hormones as the whole story.
Common PS 101 Unit 3 mistakes, and how to avoid them
Biological basis papers lose points by trying to describe the whole nervous system instead of one chain. Another frequent mistake is vague anatomy, for example describing one brain area as the control room for a whole behavior. Students often cite no evidence beyond the textbook or fail to say whether a study was done in animals or humans. Some present a correlation in hormone levels as proof of cause. Others never state where biology stops explaining, which the unit expects. Health information about yourself or relatives does not belong in the paper. If you need help narrowing a behavior to one traceable chain, our writers can draft a focused paper around it.
Get a PS 101 Unit 3 example written to your instructions
Upload your Unit 3 instructions together with the PS 101 rubric and whichever behavior or system the assignment specifies. We write a custom example that fixes the behavior first, walks the pathway with function attached at every step, cites each link separately and closes on what biology leaves unexplained. First custom sample free, back in 24 to 48 hours.
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PS 101 Unit 3 questions, answered
How much anatomy does the paper need?
Only what the chain you are explaining actually uses. A paper covering four structures thoroughly reads better than one naming fifteen, and introductory rubrics generally reward the connection between a structure and a behavior rather than breadth of coverage. If your instructions specify regions or systems, follow them, and drop anything that does not carry part of the explanation.
Is a textbook enough, or do I need journal articles?
Your instructions decide, and many introductory sections accept the course text plus one or two scholarly sources. What rarely passes is a news item or a wellness site used to support a claim about mechanism, because those compress findings past the point where the original claim survives. Where a chapter cites a study you want to use, look at the study rather than the summary.
Can I use my own medical records as the example?
Leave them out. Your chart, a relative's history, a prescriber's notes and anything a clinic holds are protected records, and a graded paper is read by people with no business seeing them. There is also a register problem: a biology paper built on your own treatment starts reading as a case about you rather than as an account of evidence. Work from published material.
Where can I find a free PS 101 Unit 3 sample paper?
Read the whole PS 101 Unit 3 biological basis paper on this page without charge, including the hormone chain, the evidence table and margin notes. Tracing a different behavior? Email the instructions and a paper built around it comes back free, often within two days.
How much anatomy does PS 101 Unit 3 need?
Only as much as the chain requires. The sample names the stomach, the arcuate nucleus of the hypothalamus, the vagus nerve and fat cells, each with what it contributes, and leaves the rest of the brain out.